Variable resistor



April 28, 1959 w. w. GRAUSTEIN, JR 2,884,505

VARIABLE RESISTOR Filed March l2, 1956 2 Sheets-Sheet 1 Y IN V EN TOR.

BY MMM April 28, 1959 w. w. GRAusTElN, JR v 2,884,506

VARIABLE REsIsToR Filed March 12, 1956 2 Sheets-Sheet 2 152 /Jzf A56 /ff f y /50/ 940/ 118/ f/o /20/ J2e IN VEN TOR. Illa tef IIL. Grau stef/z, c//Z' United States Patent() VARIABLE RESISTR Walter W. Graustein, Jr., Bolton, Mass., assgnor to Carter Manufacturing Corporation, Hudson, Mass., a corporation of Massachusetts Application March 12, 1956, Serial No. 570,846

Claims. (Cl. 201-56) The present invention relates to variable resistors, and particularly variable resistors useful in electronic devices.

Most conventional variable resistors employ a cylindrical resistance card mounted within a cylindrical casing which journals a shaft on the axis of the resistance card. A slidable electrical Contact is mounted to the shaft and slidably abuts the resistance card. lOne or both ends of the resistance card are connected to electrical terminals, or leads which extend out of the casing, and an electrical connection is also provided to the slidable contact mounted on the shaft.

ln the past, variable resistors have been relatively lange. It is conventional for the diameter of the casing of such conventional resistors to be in excess of one inch, and not uncommon for the length of the casing to exceed one inch. The electronic industry has made ygreat strides in recent years to reduce the physical size of electronic devices while maintaining the electrical characteristics of the devices, this process being known as miniaturization. Miniaturization has been achieved for electronic devices through the miniaturization of the components used in the devices, particularly the development of the transistor which greatly reduces the size of electronic units requiring electron valves.7 Variable resistors are gener ally required to achieve control over electronic circuits, and the inability of the electronic parts manufacturers to provide miniature Variable resistors has impeded the progress of miniaturization.

lt is one of the objects of the present invention to pro vide a variable resistor which is smaller than the varia-ble resistors heretofore known. The inventor achieves this object by providing a variable resistor which may be more readily assembled than the variable resistors previously known. lOften close tolerancesare required between the parts used to provide electrical contacts between a terminal mounted upon the casing of the variable resistor and the slidable electrical contact abutting the resistance card. ln most conventional constructions, an electrically conducting ring is mounted coaxially to the shaft and slip contacts mounted on the casing slide in Contact with the electrically conducting ring as it rotates with the shaft relative to the casing. lIt is a further object of the present invention to provide a Variable resistor with improved means to connect the slidabie contact abutting the resistance card to a terminal mounted tothe casing, this improved means being simpler and requiring looser tolerances.

Further objects and advantages of the present invention will be readily apparent from a further reading of this disclosure, particularly when viewed in the light of the drawings, in which:

Figure 1 is an elevational View of a variable resistor constructed according to the teachings of the present invention;

Figure 2 is a longitudinal sectional View of the variable resistor illustrated in Figure l;

Figure 3 is a sectional View taken along the line 3 3 of Figure 2;

Figure 4 is a fragmentary sectional view taken along the line 4 4 of Figure 2;

Figure 5 is a sectional view taken along the line 5 5 of Figure 2; and

Figure 6 is a longitudinal sectional view of a variable resistor constituting another embodiment of the invention.

The variable resistor illustrated in the figures has a housing 10 constructed in two portions, a drum 12 and a cover 14, both of which are electrically non-conducting. The drum 12 has cylindrical ends 16 and 18, and a protruding flange 20 disposed therebetween. The ange 20 is annular in form and is provided with a shoulder 22 confronting the cylindrical end 18 of the drum 12.

The cover 14 is cup shaped and has a cylindrical open end 24 which abuts the flange 20 and the shoulder 22 thereof. A layer of cement 26 is disposed between the cover 14 and the drum 12 adjacent to the open end of the cover 14 to secure the drum 12 to the cover 14, thus forming a cavity 28 within the housing 10.

The drum 12 is provided with an axial bore 30, and a shaft 32 is journalled within the bore 30. The shaft 32 is constructed of electrically conducting materials and provided with an axial channel 34 which extends through the shaft 32. The end of the shaft 32 within the cavity 28 is provided with a hub 36 which extends outwardly from the shaft 32 and abuts the end of the drum 12. ".,The other end of the shaft 32 is provided with a groove 38 adjacent to the end of the drum 12, and a lock washer 40 is seated within the ygroove 38.

The cover 14 is provided with an annular groove 42 which confronts the flange 20 of the drum 12. A cylindrical resistance card 44 is disposed about the cylindrical end 18 of the drum 12 and extends into the groove 42 in the cover 14. The resistance card 44 is mounted to the cylindrical end 18 of the drum fby a layer of cement 46 disposed between the resistance card 44 and the cylindrical end 18 of the drum 12. The resistance card 44 has a strip 48 of electrically insulating material disposed in cylindrical form. A plurality of turns of resistance wire 50 are disposed transversely about the strip 48. The turns of resistance wire 50 are secured to the strip 48 of insulating material by a layer 52 of electrically insulating cement.

The hub 36 at the end of the shaft 32 is provided with a groove 54 about its periphery. A wire shaped contact 56 has an annular portion 57 disposed within the -groove 54 and fastened to the shaft 32 by crimps 58. The contact 56 also has a protruding bend, or loop, 59 which abuts a band 60 of the surface of the resistance card 44 which confronts the `groove 54 in the hub 36, all electrical insulation being removed from the band 60 thus exposing each turn of wire 50 to the bend 59 as it traverses this band 60. Thus for all rotational positions, the contact 56 makes electrical contact with one of the wires 50 of the resistance card and with the shaft 32.

The cover 14 is provided with an indentation 62 confronting the channel 34 in the shaft 32, and an aperture 64 pierces the cover 14 in alignment with the channel 34. An electrically conducting eyelet 66 has a ange 68 and a stem 70 and is disposed with the ange 68 in the indentation 62 and the stem 70 extending through the aperture 64 in the cover 14. A passageway 72 extends along the axis of the eyelet 66, and the straight portion 74 of an electrically conducting rod 76 is secured to the eyelet 66 within the passageway 72, for example by a crimp 73 in the stem 70. The rod 76 has a serpentine end portion 78 which is disposed within the channel 34 of the shaft 32. The serpentine end portion 78 is formed by a plurality of bends 80 within the channel 34 forming contact 3 points 82 which are in slidable abutment with the shaft 32. At least two contact points 82 are required, and in the embodiment illustrated in the figures there are four contact points.

The drum 12 and cover 14 are constructed of electrically insulating materials, such as polyethylene plastic. The shaft 32 and eyelet 66 are constructed of electrically conducting materials, such as brass, and the rod 76 is constructed of electrically conducting material of relatively high elasticity and relatively good electrical conductivity, such as brass coated with solder. As a result of this construction, the contact 56 which is in electrical contact with one of the turns of resistance wire 50 on the resistance card 44 is connected to the eyelet 66, and hence the exterior of the housing 10. j

The end 18 of the drum 12 is provided with a ridge 84 which is generally parallel to the axis of the bore 30 in the drum and which extends from a point adjacent to the ange 20 to the cavity 28. The drum 12 is provided with a pair of cylindrical recesses 86 on opposite sides of the ridge 84 and adjacent to the ange 20. A pair of electrically conducting rods 88 are also disposed on opposite sides of the ridge 84 and have end portions 90 disposed normal to the axis of the rods. The rods 88 are mounted to the drum 12 with their end portions 90 anchored within the recesses 86. Each of the rods 88 extends through an orifice 92 in the end of the cover 14. The rods 88 are electrically connected to the end turns of resistance wire 50 on the resistance card 44, and hence form terminals external to the housing of the variable resistor.

A knob 94 is provided with an annular recess 96 therein and an axial pin 98 which extends through the recess 96 into the channel 34 within the shaft 32. The pin 98 is press tted into the channel 34 to secure the knob 94 to the shaft 32. The knob 94 is also provided with shoulders 99 which abut the surface of the washer 40, and a layer of cement 100 is disposed between the shoulders 99 and the washer 40 to aid in securing the knob 94 to the shaft 32. l

The end 16 of the drum 12 is provided with an outwardly extending ridge 104, and the knob 94 is provided with a ridge 106 extending into the cavity 96 thereof. Rotation of the knob 94 causes the ridges 104 and 106 to abut each other, thereby providing stops to rotation.

When assembling the variable resistor described above, the drum 12 forms the foundation about which the other elements of the resistor are assembled. First, the shaft 32 is inserted through the bore 30 of the drum 12, and the washer 40 is placed in position, the end of the shaft 32 being wedged outwardly to secure the shaft and washer when the contact 56, which has previously been mounted to the hub 36, is properly oriented. Next, the preformed resistance card 44 is cemented to the end portion 18 of the drum 12, held in position and baked. The serpentine portion 78 of the rod 76 is secured in the chanenl 34 of the shaft 32. The layerv 26 of cement is applied to the drum 12, and the cover is then slipped into position, the rod 76 sliding through the eyelet 66 and the rods 88 sliding through the apertures 92 in the cover 14. It is thus clear, that this construction greatly facilitates assembly and permits miniature variable resistors to be readily constructed. The inventor has found that variable resistors with an outer diameter of Mi inch and a length of approximately 0.430 inch may readily be constructed in this manner and have resistances continuously variable over a range from Oto 50,000 ohms, for example.

Figure 6 illustrates a modified form of the present invention. In the resistor here illustrated, a cylindrical drum 110 is provided with a cylindrical ange 112 coaxially thereabout adjacent to one end thereof. A cylindrical resistance card 114 is secured coaxially about the longer portion of the drum 110 and extends slightly beyond the end 115 of the drum 110. The drum 110 is provided with an axial bore 116, and a solid shaft 118 is rotatively disposed within the bore 116. An electrically conducting hub 120 is disposed at one end of the shaft 118 and abuts the end 115 of the drum 110. The edge of the resistance card 114 which extends beyond the drum, designated 122 is free of electrical insulation, and an electrical contact 124 slidably abuts this edge 122 of the resistance card 114 and is secured to the hub 120 of the shaft 118. This contact 124 is constructed of spring material. A second contact 125, also secured to the hub 120, is provided with a U-shaped bend 126 adjacent to the hub 120. An outwardly extending loop 128 is disposed at this end of the contact 125 and abuts a at surface 130 of an electrical terminal 132. The two contacts 124 and 125 may of course be constructed of a single member of electrically conducting spring material, as indicated by the dotted line in Figure 6. The electrical terminal 132 is mounted in an aperture 134 in a nonconducting end cap 136 which forms a part of a housing 138 for the resistor. The end cap 136 is secured within a cylinder 140 which is attached to the flange 112 of the drum 110, thus forming the housing 138.

Leads 142 attached to the ends of the resistance card 114 extend through apertures 144 in the end cap 136 in a manner similar to the lead 88 of the rst embodiment of the invention. Also, a stop washer 146 is secured to the end of the shaft 118 opposite the hub 120, and provided with a tab 148 extending toward the flange 112 of the drum 110. The drum 110 is also provided with a ridge 150 between the ange 112 and the washer 146 which abuts the tab 148 to form a rotational stop. A knob 152 is cemented to the washer 146 by a layer of cement 154.

It is clear that in this construction of the invention, the drum 110 supports the resistance card 114 throughout a larger portion of its length which is possibly due to the fact that the contact 124 slidably abuts the edge 122 of the resistance card 114, rather than the side of the resistance card as in the previous embodiment. Further, this embodiment of the invention is also relatively easily assembled. The resistance card 114 is mounted to the drum 110 before the shaft 118 is secured within the drum 110 and the contact 124 placed in abutment with the edge 122 of the resistance card 114. Itis then only necessary to place the housing 138 about the resistance card 114 and drum 110 and secure the housing 138 to the ange 112. The end cap 136 may either have been secured within the cylinder 140 of the housing 138 before the cylinder is installed, or may be inserted thereafter.

The invention claimed is:

1. A variable resistor comprising, in combination, a cylindrical drum having an axial bore, a shaft constructed of electrically conducting material journalled within the i bore and provided with an outwardly extending hub at one end abutting the drum, and the hub being provided with a circumferential groove thereabout, -a cylindrical resistance card mounted coaxially to the periphery of the drum and extending outwardly from one end of the drum to confront the hub, and an electrically conducting Wire having an annular portion secured within the groove in the hub and an outwardly extending loop slidably abutting the confronting surface of the resistance card.

2. A variable resistor comprising, in combination, a cylindrical drum having an axial bore, a shaft constructed of electrically conducting material journalled within the bore and provided with an axial channel, said shaft also being provided with an outwardly extending hub at one end abutting the drum, and the hub being provided with a circumferential groove thereabout, a cylindrical resistance card mounted coaxially to the periphery of the drum and extending outwardly from one end of the drum to confront the hub, yan electrically conducting wire having an annular portion secured within the groove in the hub and an outwardly extending loop slidably abutting the confronting surface of the resistance card, and an electrically conducting rod mounted to the drum and partially disposed within the channel in the shaft, said rod having at least two adjacent bends in opposite directions within the channel in slidable contact with the shaft.

3. A variable resistor comprising, in combination, a cylindrical drum having an axial bore and a circumferential flange thereabout, said flange having a shoulder confronting one end or" the drum, a cup shaped cover disposed about said end of the drum and secured to the shoulder on the ange thereof, a shaft constructed of electrically conducting material journalled within the bore, :said shaft being provided with an outwardly extending hub abutting the end of the drum disposed within the cover and provided with a circumferential groove, a cylindrical resistance card mounted coaxially to the periphery of the drum between the drum and the cover and extending beyond the end of the drum to confront the hub, a wire shaped electrically conducting contact having an annular portion secured within the groove and an outwardly extending loop slidably abutting the confronting portion of the lresistance card.

4. A variable resistor comprising, in combination, a cylindrical drum having an axial bore and a circumferential ange thereabout, said flange having a shoulder confrontinU one end of the drum, a cup shaped cover disposed about said end of the drum and secured to the shoulder en the flange thereof, a shaft constructed of electrically conducting material having an axial channel journalled within the bore, said shaft being provided with an outwardly extending hub abutting the end of the drum disposed within the cover and provided with a circumferential groove, a cylindrical resistance card mounted coaxially to the periphery of the drum between `the drum and the cover and extending beyond the end of the drum, a wire shapel electrically conducting contact having an annular portion secured within the groove and an outwardly extending loop slidably abutting the confronting portion of the resistance card, and an electrically conducting rod mounted to the cover and extending into the channel in the shaft, said rod having at least two adjacent bends in opposite directions within the channel in slidable contact with the shaft.

5. A variable resistor comprising a housing having a cylindrical cavity therein, a shaft provided with an axial channel therein rotatably disposed on the axis of the cavity, a cylindrical resistance card disposed in the cavity coaxially with the shaft, an electrical contact mounted to the shaft and electrically connected thereto, said contact slidably abutting the resistance card, and an electrically conducting rod mounted to the cover and extending into the channel in the shaft, said rod having at least two adjacent bends in opposite directions within the channel in slidable contact with the shaft.

6. A variable resistor comprising a housing constructed of electrically insulating material having a cylindrical cavity therein, a shaft provided with an axial channel Itherein rotatably disposed on the axis of the cavity, a cylindrical resistance card disposed in the cavity coaxially with the shaft, an electrical contact mounted to the shaft and electrically connected thereto, said contact slidably abutting the resistance card, an electrically conducting terminal mounted to the housing provided with a hollow stem extending through the housing axially with the channel in the shaft, and an electrically conducting rod having two portions, one portion extending into the channel of the shaft and having at least two adjacent bends in opposite directions within the channel in slidable contact with the shaft, and the other portion extending through the hollow stem of the terminal to the exterior of the housing.

7. A variable resistor comprising, in combination, a cylindrical drum having an axial bore and a circumferential flange thereabout, a cylindrical resistance card disposed coaxially about the drum, a shaft journaled within the bore of the drum, an electrically conducting contact secured to the shaft adjacent to the end of the drum and abutting the edge of the resistance card, a cup shaped cover secured to the flange and extending about the resistance card, an electrical contact having a surface confronting the shaft and normal to the axis thereof, and a second electrical contact mounted to the shaft and electrically connected to the first electrical contact slidably abutting the surface of the terminal.

8. A variable resistor comprising, in combination, a cylindrical drum having an axial bore and a circumferential ange thereabout, a cylindrical resistance card disposed coaxially about the drum, a shaft journaled within the bore of the drum, an electrically conducting contact secured to the shaft adjacent to the end of the drum and abutting the edge of the resistance card, a cup shaped cover secured to the tiange and extending about the resistance card, an electrical conductor extending through the cover, and means for making electrical contact between the conductor and the first electrical contact.

9. A variable resistor comprising, in combination, a cylindrical drum having an axial bore and a circumferential flange thereabout, a cup shaped cover disposed about one end of the drum and secured to the flange thereof, a shaft journaled within the bore having an electrically conducting hub slidably abutting the drum between the drum and the cover, an electrically conducting member constructed of spring material secured to the hub and slidably abutting the confronting edge of the resistance card, said member having a U-shaped bend adjacent to the end opposite the end abutting the resistance card and extending across the axis of the shaft, an electrical terminal secured to the cover and extending therethrough having a at electrically conducting surface on the axis of the shaft and normal thereto, said surface being in slidable contact with the end of the contact opposite to the resisance card.

10. A variable resistance comprising the elements of claim 8 in combination with a washer secured to the end of the shaft opposite the electrical contact, said washer having a tab extending toward the ange of the drum adjacent to the periphery thereof, and said drum being provided with an outwardly extending ridge adapted to abut the tab to form a rotational stop.

References Cited in the le of this patent UNITED STATES PATENTS 870,042 MacLagan Nov. 5, 1907 1,561,137 Burns Nov. 10, 1925 2,657,295 Barclay Oct. 27, 1953 

